1. Field of the Invention
The present invention relates to an optical fiber, a tape-like optical fiber that are used for an optical transmission path inside a device or between devices, and an optical module using the same.
2. Description of the Related Art
As optical transmission technology inside a device or between devices, optical transmission according to an optical interconnection system attracts attention. In such optical interconnection system, an array-shaped optical device such as VCSEL (Vertical-Cavity Surface-Emitting Laser) that can be easily used for a multi-channel array has been generally used as an optical device. As the optical interconnection system, for example, Japanese Patent Laid-Open No. 2006-310197 (JP-A 2006-310197) discloses a system for connecting between devices by means of an optical cable. For example, Japanese Patent Laid-Open No. 2007-256372 (JP-A 2007-256372) discloses an end face of the optical fiber in the complex cable is connected to an optical device.
As the conventional optical fiber used for optical transmission between array-shaped optical devices such as the VCSEL, for example, a singe-core optical fiber 94 with a structure shown in FIG. 9A, and a multi-core optical fiber (tape-like optical fiber) 96 with a structure shown in FIG. 9B have been used. The single-core optical fiber 94 comprises a core 90, a clad 91, a low Young modulus layer (inner coating layer) 92 having Young modulus of 10 MPa or less and provided around the clad 91, and a high Young modulus layer (outer coating layer) 93 having Young modulus of 100 MPa or more and provided around the low Young modulus layer 92. The multi-core optical fiber 96 comprises a plurality of the single-core optical fibers 94 that are aligned in one column (geometrically in parallel), and the high Young modulus layer (coating layer) 95 having Young modulus of 50 MPa or more and coating the aligned single-core optical fibers 94.
In general, the single-core optical fiber 94 or the tape-like optical fiber 96 is used after its terminal is connected and bonded to a connector and the end face of the connector is polished, in order to be optically connected to devices such as light emitting device, light receiving device, lens, and optical fiber.
For forming a connector from the single-core optical fiber 94, the single-core optical fiber 94 should be inserted into a ferrule. As shown in FIGS. 10A to 10C, a conventional ferrule 100 comprises an optical fiber insertion hole 101 which has an inner diameter greater than an outer diameter of the single-core optical fiber 94 including the inner and outer coating layers 92, 93 and is provided on a side of one end of the ferrule 100, and a light input/output bore 103, which has an inner diameter substantially corresponding to an outer diameter of the clad 91 of the single-core optical fiber 94 (i.e. slightly greater than the outer diameter of the clad 91), and inputs and outputs a light at an end face of another end part 102 of the ferrule 100, in which the optical fiber insertion hole 101 communicates with the light input/output bore 103. As shown in FIG. 11, after inserting an optical fiber composed of the core 90 and the clad 91, the coating (the low Young modulus layer 92 and the high Young modulus layer 93) of which was removed, into the light input/output bore 103 arranged on the other end part 102 of the ferrule 100, and the single core optical fiber 94 is fixed by an adhesive material 110 inside the ferrule 100. After that, a bottom surface 111 which is a light input/output end face of the ferrule 100 is polished.
The multi-core optical fiber 96 has a structure similar to the structure of the single-core optical fiber 94. The high Young modulus layer 95 which collectively coats the multi-core optical fiber 96 is removed, and respective cores are separated from each other. Thereafter, the multi-core optical fiber 96 is inserted into the ferrule, in which bores of the number corresponding to the number of the single-core optical fibers 94 are formed, and terminal-processed similarly to the structure shown in FIG. 11.